Oocyte maturation arrest Metaphase II oocyte maturation arrest 2025-10-06T08:03:46Z The morphologic classification of MII generally denotes an oocyte that is mature, having arrested in metaphase II and is presumed to be capable of fertilization. However, there are subsets of women who produce oocytes with MII morphology that are not capable of embryo formation even with fertilization. This incongruence between morphologic maturity and capacity could be attributed to either the inclusion within the morphologic classification immature oocytes arrested at any stage between PBI formation and metaphase II, which are not capable of fertilization, or oocytes arrested normally at metaphase II that do not possess the ability to complete meiosis. Oocyte arrest at metaphase II Metaphase II oocyte meiotic arrest